A new study from Brazil found that while individuals having darker skin tones are better protected against UV light, they also are more prone to vitamin D deficiency.

"Our findings suggest that skin tanning, which is a natural protection against the harmful effects of UV irradiation, limits the progressive rise in serum vitamin D toward optimal concentrations," said lead study author Francisco Bandeira, M.D., Ph.D. Bandeira is the associate professor of medicine and chief of the Division of Endocrinology and Diabetes at the University of Pernambuco Medical School in Recife, Brazil.

According to Bandeira, her research showed that individuals living in tropical regions (within eight degrees south of the equator) had higher rates of sun exposure and UV irradiation, and most individuals showed serum vitamin D deficiency.

Running the Numbers

Bandeira and co-researchers evaluated 986 individuals, ages 13 to 82, who lived in the city of Recife, Brazil. There was roughly an equal number of males and females and all participants had high rates of daily sun exposure.

Furthermore, the participants did not use sunscreen or take vitamin D supplements on a regular basis. Typically, individuals with higher Fitzpatrick skin types (meaning darker skin tones) have an easier time tanning and achieving a deeper color rather than burning.

The researchers calculated the sun index, which is the number of hours of sun exposure per week multiplied by the fraction of body surface area exposed.

Serum vitamin D levels were measured and compared with the skin phototype and sun index scores.

Outcome: Sun Up, D Down

Individuals having more sun exposure and tanner skin showed less vitamin D deficiency than other participants. However, most participants with high daily exposure had serum vitamin D levels below the normal cutoff, which is 30 ng/mL, explained Bandeira.

The participants with deficient serum vitamin D were older and had lower sun index values, as opposed to participants with normal levels. In total, 72% of participants were vitamin D deficient, with a mean level of 26.06 ng/mL.